Here is an excellent article on yoniso manasikara or wise reflection. I highly, highly recommend this read:

Wise Reflection:The Importance ofWise Reflection in Meditation

The purpose of this essay is to explain the value of wise reflection, yoniso manasikara, and to encourage readers to use their own thought processes for the growth of wisdom in their formal meditation practice. The majority of experienced Buddhist meditators whom I have met during thirty years of meditation and eighteen years of teaching were unfamiliar with formal reflective meditation. By way of this essay I hope to correct this lack of understanding.

The Buddha himself greatly stressed the importance of wise reflection. In an important discourse on the topic of wise reflection, the Sabbasava Sutta (MN 2), the Buddha says:

“I say that the getting rid of anxieties and troubles is possible for one who knows and sees, not for one who does not know and see. What must one know and see in order to get rid of anxieties and troubles? Wise reflection and unwise reflection.

For one who reflects unwisely, there arise anxieties and troubles that have not yet arisen, and those that have already arisen increase. But for one who reflects wisely, anxieties and troubles that have not yet arisen do not arise, and those already arisen disappear.”

What is yoniso manasikara? Yoniso manasikara is a Pali term that can be translated as wise reflection. This includes systematic attention, careful attention, reasoned attention, having thorough method in one’s thought, proper consideration, wise consideration, critical reflection, analytical reflection, or thinking in terms of causal relations or by way of problem solving. Yoniso manasikara is a significant factor leading to the arising of insight or wisdom.

What causes our mental suffering? Simply stated, it is wrong thinking that produces our mental dukkha (suffering). Right thinking will end our mental dukkha. Thus, it is important to use formal reflective meditation in order to develop right thinking.

In helping the reader to understand the importance of reflective meditation, much of this booklet is devoted to trying to correct meditation “myths.” By “myths” I mean certain misunderstandings that many Buddhists have acquired. These misunderstandings are widespread, and as a result, many meditators do not realise the importance of reflective meditation and may even doubt some of the things written here. To support my understanding, I have included several relevant teachings from the scriptures that emphasize the importance of wise reflection.

For any of you who may experience doubts concerning what is written here, I ask you to follow the Buddha’s advice to all of us, to seek the truth in order to dispel ignorance. If you are going to follow the Buddha in this way, then it is important that you stay open to what is presented. If you stay open, yet after reading find that you still have remaining doubts, feel free to contact me at the address at the end of this booklet. I welcome any wise discussion on anything presented here. I do believe, though, that if you are seriously interested in ending your mental dukkha, then what is written here will help you greatly.

The heart of the path is SO simple. No need for long explanations. Give up clinging to love and hate, just rest with things as they are. That is all I do in my own practice. Do not try to become anything. Do not make yourself into anything. Do not be a meditator. Do not become enlightened. When you sit, let it be. When you walk, let it be. Grasp at nothing. Resist nothing. Of course, there are dozens of meditation techniques to develop samadhi and many kinds of vipassana. But it all comes back to this - just let it all be. Step over here where it is cool, out of the battle. - Ajahn Chah

If you have asked me of the origination of unease, then I shall explain it to you in accordance with my understanding: Whatever various forms of unease there are in the world, They originate founded in encumbering accumulation. (Pārāyanavagga)

Exalted in mind, just open and clearly aware, the recluse trained in the ways of the sages:One who is such, calmed and ever mindful, He has no sorrows! -- Udana IV, 7